An MRI apparatus using a superconducting magnet includes a cryocooler that condenses helium gas vaporized in a liquid helium vessel back to liquid helium again by cooling. Although maintaining pressure in the helium vessel constant is recommended, vaporized liquid helium is liquidized more than needed if a cooling capacity of the cryocooler is too high, which results in too low pressure in the vessel. Therefore, a configuration to maintain pressure in the helium vessel constant by disposing a heater in the vessel to vaporize liquid helium in the vessel as needed is generally adopted.
Also, PTL 1 suggests a technique of increasing or decreasing a cooling capacity itself of a cryocooler when pressure in a vessel is nearing an upper limit value and a lower limit value of predetermined pressure in order to solve a problem in which power consumption of an MRI apparatus rises due to a heater in a helium vessel.
In order to change a cooling capacity, PTL 1 discloses a method to change a frequency of a cooling cycle, a method to stop actions by stopping power supply to a cryocooler, and a method to adjust an amount of compressed helium gas supplied to a cryocooler.